During my post-doctoral fellowship, I have continued my interest in the neuroendocrine control of reproduction and the mechanism by which the gonadotrope decodes the pulsatile GnRH signal, released from GnRH neurons in the hypothalamus. This award will provide the opportunity to meet my long-term goal of becoming an independent investigator, supplementing the leadership, research, and ethical training programs offered by Brigham and Women's Hospital. Production of pituitary FSH and LH, under the control of pulsatile GnRH, is essential for fertility. Pituitary FSH-subunit (FSH) transcription and hence FSH secretion are preferentially stimulated at slow rather than fast frequencies of pulsatile GnRH, in contrast to LH. The mechanisms for this disparity are not known. The goal of this project is to elucidate the underlying mechanisms that contribute to the GnRH pulse frequency-dependent differential control of FSH transcription and subsequent FSH synthesis. Using our perifusion system and the murine gonadotrope-derived LT2 cell line model, we have shown previously that GnRH activation of CREB mediates preferential induction of FSH at slower GnRH pulse frequencies, whereas ICER is induced at high GnRH pulse frequencies and antagonizes the stimulatory effects of CREB. The molecular mechanisms by which pulsatile GnRH regulates CREB and ICER expression, activation, and regulation remain poorly understood. I propose to extend our prior in vitro observations in cell lines to in vivo mouse models, and predict that gonadotrope-specific CREB and ICER deficient mouse models will further demonstrate the critical function of these transcription factors in decoding oscillatoy GnRH signals from the hypothalamus, by demonstrating disrupted cyclicity and impaired reproductive function. The specific objectives are to determine the manner in which two transcription factors, cAMP response element binding protein (CREB) and inducible cAMP early repressor (ICER), mediate the differential response of FSH to pulsatile GnRH in the gonadotrope to contribute to reproductive function. To achieve these objectives, the following aims are proposed: 1) Investigate the mechanisms by which PKA activity and CREB phosphorylation status are regulated by pulsatile GnRH to preferentially stimulate FSH transcription at slow versus fast frequencies; 2) Investigate the pathways that regulate ICER synthesis, action and degradation in a GnRH pulse frequency-dependent manner; 3) Study the effect of CREB and ICER gene disruption in gonadotropes on FSH transcription and reproductive function in vivo. The elucidation of the mechanisms by which FSH transcription is regulated by pulsatile GnRH could provide novel therapeutic targets for reproductive disorders such as polycystic ovarian syndrome (PCOS) and hypothalamic amenorrhea (HA).